/*
 * Copyright [2013-2021], Alibaba Group Holding Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.calcite.plan;

import org.apache.calcite.rel.RelNode;



/**
 * The digest is the exact representation of the corresponding {@code RelNode},
 * at anytime, anywhere. The only difference is that digest is compared using
 * {@code #equals} and {@code #hashCode}, which are prohibited to override
 * for RelNode, for legacy reasons.
 *
 * <p>INTERNAL USE ONLY.</p>
 */
public interface RelDigest {
    /**
     * Reset state, possibly cache of hash code.
     */
    void clear();

    /**
     * Returns the relnode that this digest is associated with.
     */
    RelNode getRel();
}

